Retardation optical element, and method of producing the same, and polarization element and liquid crystal display, each including retardation optical element

ABSTRACT

Provided herein is a retardation optical element  10  that produces no bright and dark fringes on a displayed image even when placed between a liquid crystal cell  104  and a polarizer  102 B and thus can effectively prevent lowering of display quality. The retardation optical element  10  includes a retardation layer  12  having a cholesteric-regular molecular structure with liquid crystalline molecules in planar orientation. The helical pitch in the molecular structure of the retardation layer  12  is so adjusted that the retardation layer  12  can, owing to its molecular structure, selectively reflect light whose wavelength falls in a range different from the wave range of light incident on the retardation layer  12  (the selective reflection wave range of the retardation layer is either shorter or longer than the wave range of the incident light). Further, the retardation layer  12  has two opposite main surfaces (larger surfaces)  12 A and  12 B that are perpendicular to each other in the direction of thickness, where the directions of the directors Da of the liquid crystalline molecules on the entire area of the one surface  12 A are substantially the same, and those of the directors Db of the liquid crystalline molecules on the entire area of the other surface  12 B are also substantially the same.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a retardation optical elementfor use in a liquid crystal display or the like, especially aretardation optical element that includes a retardation layer having acholesteric-regular molecular structure and can compensate for the stateof polarization of light that slantingly emerges from a liquid crystalcell in the direction deviating from its normal, to a method ofproducing the retardation optical element, and to a polarization elementand a liquid crystal display, each including the retardation opticalelement.

[0003] 2. Description of Related Art

[0004]FIG. 13 is a diagrammatic exploded perspective view of aconventional, general liquid crystal display.

[0005] As shown in FIG. 13, the conventional liquid crystal display 100includes a polarizer 102A on the incident side, a polarizer 102B on theemergent side, and a liquid crystal cell 104.

[0006] Of these component parts, the polarizers 102A and 102B are soconstructed that they selectively transmit only linearly polarized lighthaving the plane of vibration in a predetermined direction, and arearranged in the cross nicol disposition so that the direction ofvibration of the linearly polarized light transmitted by the polarizer102A is perpendicular to that of vibration of the linearly polarizedlight transmitted by the polarizer 102B. The liquid crystal cell 104include a large number of cells corresponding to pixels, and is placedbetween the polarizers 102A and 102B.

[0007] A case where the liquid crystal cell 104 in the above-describedliquid crystal display 100 is of VA (Vertical Alignment) mode, which anematic liquid crystal having negative dielectric anisotropy is sealedin a liquid crystal cell, is now taken as an example. Linearly polarizedlight that has passed through the polarizer 102A on the incident sidepasses, without undergoing phase shift, through those cells in theliquid crystal cell 104 that are in the non-driven state, and is blockedby the polarizer 102B on the emergent side. On the contrary, thelinearly polarized light undergoes phase shift when it passes throughthose cells in the liquid crystal cell 104 that are in the driven state,and the light in an amount corresponding to the amount of this phaseshift passes through and emerges from the polarizer 102B on the emergentside. It is therefore possible to display the desired image on thepolarizer 102B side (i.e., on the emergent side by properly controllingthe driving voltage that is applied to each cell in the liquid crystalcell 104. The liquid crystal display 100 is not limited to the aboveembodiment in which light is transmitted and blocked in theabove-described manner, and there is also a liquid crystal display soconstructed that light emerging from those cells in the liquid crystalcell 104 that are in the non-driven state passes through and emergesfrom the polarizer 102B on the emergent side, and that light emergingfrom those cells that are in the driven state is blocked by thepolarizer 102B on the emergent side.

[0008] Discussion is now made on a case where linearly polarized lightpasses through the non-driven-state cells in the above-described liquidcrystal cell 104 of VA mode. The liquid crystal cell 104 isbirefringent, and its refractive index in the direction of thickness andthat in the direction of plane are different from each other. Therefore,of the linearly polarized light that has passed through the polarizer102A on the incident side, the light that has entered the liquid crystalcell 104 along its normal passes through the liquid crystal cell 104without undergoing phase shift, but the light that has slantinglyentered the liquid crystal cell 104 in the direction deviating from itsnormal undergoes phase shift while it passes through the liquid crystalcell 104, and becomes elliptically polarized light. The cause of thisphenomenon is that those liquid crystalline molecules that arevertically aligned in the liquid crystal cell 104 when the cells in theliquid crystal cell 104 of VA mode are in the non-driven state functionas a positive C plate. It is noted that the amount of phase shift thatoccurs for light passing through the liquid crystal cell 104(transmitted light) is affected also by the birefringence of the liquidcrystalline molecules sealed in the liquid crystal cell 104, thethickness of the liquid crystal cell 104, the wavelength of thetransmitted light, and so on.

[0009] Owing to the above-described phenomenon, even when the cells inthe liquid crystal cell 104 are in the non-driven state and linearlypolarized light is supposed to be transmitted through the liquid crystalcell 104 as it is and blocked by the polarizer 102B on the emergentside, a part of the light that emerges slantingly from the liquidcrystal cell 104 in the direction deviating from its normal is to leakfrom the polarizer 102B on the emergent side.

[0010] For this reason, the above-described conventional liquid crystaldisplay 100 has the problem (so-called viewing angle dependency problem)that the display quality at the time when an image is viewed slantinglyfrom a position not on the normal of the liquid crystal cell 104 islower than that at the time when the image is viewed from the front ofthe display.

[0011] To eliminate the viewing angle dependency problem of theaforementioned conventional liquid crystal display 100, there have beendeveloped a variety of techniques up to now. One of them is the liquidcrystal display described, for example, in Patent Document 1 (JapaneseLaid-Open Patent Publication No. 67219/1991). This liquid crystaldisplay uses a retardation optical element including a retardation layerhaving a cholesteric-regular molecular structure (a retardation layerhaving double refractivity), where the retardation optical element isplaced between a liquid crystal cell and a polarizer in order to provideoptical compensation.

[0012] In the retardation optical element having a cholesteric-regularmolecular structure, the selective reflection wavelength given by theequation λ=nav·p (p: the helical pitch in the helical structureconsisting of liquid crystalline molecules, nav: the mean refractiveindex of a plane perpendicular to the helical axis), is so adjusted thatit is either shorter or longer than the wavelength of transmitted light,as described in Patent Document 2 (Japanese Laid-Open Patent PublicationNo. 322223/1992), for example.

[0013] In the aforementioned retardation optical element, linearlypolarized light that has slantingly entered the retardation layer in thedirection deviating from its normal undergoes phase shift, while passingthrough the retardation layer, to become elliptically polarized light,like in the case of the above-described liquid crystal cell. The causeof this phenomenon is that the cholesteric-regular molecular structurefunctions as a negative C plate. The amount of phase shift that occursfor light passing through the retardation layer (transmitted light) isaffected also by the birefringence of the liquid crystalline moleculesin the retardation layer, the thickness of the retardation layer, thewavelength of the transmitted light, and so on.

[0014] Therefore, the viewing angle dependency problem of conventionalliquid crystal displays can successfully be solved by the use of theabove-described retardation optical element if the retardation layercontained in the retardation optical element is properly designed sothat the phase shift that occurs in a liquid crystal cell of VA mode,which functions as a positive C plate, and the phase shift that occursin the retardation layer contained in the retardation optical element,which functions as a negative C plate, are canceled each other.

[0015] However, it has been found that the viewing angle dependencyproblem can be solved if the above-described retardation optical element(a retardation layer having a cholesteric-regular molecular structure)is placed between a liquid crystal cell and a polarizer, but that, whenthe retardation optical element is so provided, bright and dark fringescould appear on a displayed image to drastically lower the displayquality.

[0016] The inventor has made earnest studies to find the causes of thisphenomenon by conducting experiments and computer-aided simulations,and, as a result, finally found that one of the causes is the directionsof the directors of liquid crystalline molecules on the surfaces of theretardation layer contained in the retardation optical element.

SUMMARY OF THE INVENTION

[0017] The present invention has been accomplished in the light of theaforementioned drawbacks in the related art. An object of the presentinvention is to provide: a retardation optical element that produces nobright and dark fringes on a displayed image even when it is placedbetween a liquid crystal cell and a polarizer and can thus effectivelyprevent lowering of display quality; a method of producing such aretardation optical element; and a polarization element and a liquidcrystal display, each including the retardation optical element.

[0018] A retardation optical element according to the first feature ofthe present invention comprises a retardation layer having acholesteric-regular molecular structure with liquid crystallinemolecules in planar orientation, the helical pitch in the molecularstructure being so adjusted that the wavelength of light selectivelyreflected by the retardation layer due to its molecular structure fallsin a range different from the wave range of incident light, wherein thedirections of the directors of the liquid crystalline molecules on onesurface of the two opposite main surfaces of the retardation layer aresubstantially the same, and those of the directors of the liquidcrystalline molecules on the other surface of the retardation layer arealso substantially the same.

[0019] According to the first feature of the present invention, in theretardation layer having a cholesteric-regular molecular structure withliquid crystalline molecules in planar orientation, the helical pitch inthe molecular structure is so adjusted that the wavelength of lightselectively reflected by the retardation layer due to its molecularstructure falls in a range different from the wave range of incidentlight, and the directions of the directors of the liquid crystallinemolecules on each of the two main surfaces of the retardation layer aremade substantially the same. Therefore, even when the retardationoptical element is placed between a liquid crystal cell and a polarizer,it does not produce bright and dark fringes on a displayed image and canthus effectively prevent lowering of display quality.

[0020] In the retardation optical element according to the first featureof the present invention, the dispersion in the directions of thedirectors of the liquid crystalline molecules on each one of the onesurface and the other surface of the retardation layer is within ±10°,preferably within ±5°, more preferably within ±1°. As long as thedispersion falls in the above range, the appearance of bright and darkfringes is prevented more effectively, and the lowering of displayquality can thus be prevented more surely.

[0021] In the retardation optical element according to the first featureof the present invention, it is preferable that the directions of thedirectors of the liquid crystalline molecules on the one surface of theretardation layer be substantially parallel with those of the directorsof the liquid crystalline molecules on the other surface of theretardation layer. If the directions of the directors of the liquidcrystalline molecules are so made, the appearance of bright and darkfringes is more effectively prevented, and the lowering of displayquality can thus be more surely prevented.

[0022] In the above case, it is preferable that the angle made by thedirections (mean direction) of the directors of the liquid crystallinemolecules on the one surface of the retardation layer and the directions(mean direction) of the directors of the liquid crystalline molecules onthe other surface of the retardation layer be within ±10°, preferablywithin ±5°, more preferably within ±1°. As long as the angle made by thetwo mean directions falls in the above range, the appearance of brightand dark fringes is prevented more effectively, and the lowering ofdisplay quality can thus be prevented more surely.

[0023] Further, in the retardation optical element according to thefirst feature of the present invention, it is preferable that theretardation layer has a helical structure with a pitch number ofsubstantially (0.5×integer) between the directions of the directors ofthe liquid crystalline molecules on the one surface of the retardationlayer and those of the directors of the liquid crystalline molecules onthe other surface of the retardation layer. If the retardation layer hassuch a helical structure, even when the retardation optical element isplaced between a liquid crystal cell and a polarizer, no bright and darkfringes appear on a displayed image, and the lowering of display qualitycan thus be effectively prevented.

[0024] In the above case, it is preferable that the angle made by thedirections of the directors of the liquid crystalline molecules on theone surface of the retardation layer and those of the directors of theliquid crystalline molecules on the other surface of the retardationlayer be within ±10°, preferably within ±5°, more preferably within ±1°.As long as this angle falls in the above range, the appearance of brightand dark fringes is prevented more effectively, and the lowering ofdisplay quality can thus be prevented more surely. The helical pitch orpitch number in the helical structure of the retardation layer may varydepending upon position in the plane extending in parallel with the onesurface and the other surface of the retardation layer.

[0025] Further, in the retardation optical element according to thefirst feature of the present invention, it is preferable that theretardation layer be composed of successively, directly laminatedmultiple layers, each having a cholesteric-regular molecular structurewith liquid crystalline molecules in planar orientation, and that thedirections of the directors of the liquid crystalline molecules on thetwo adjacent surfaces of each two neighboring layers among the multiplelayers be substantially parallel with each other.

[0026] Furthermore, in the retardation optical element according to thefirst feature of the present invention, it is preferable that theretardation layer has a molecular structure in which chiral nematicliquid crystalline molecules are three-dimensionally crosslinked. By somaking the retardation layer, it is possible to thermally stably retainthe cholesteric-regular molecular structure.

[0027] A method of producing a retardation optical element according tothe second feature of: the present invention comprises the steps of:applying a first liquid crystal comprising at least one type ofpolymerizable monomer or oligomer molecules having cholestericregularity to an alignment layer that has been so formed that thesurface thereof exerts alignment regulation power in substantially onedirection, thereby aligning the first liquid crystal by the alignmentregulation power of the surface of the alignment layer; andthree-dimensionally crosslinking and solidifying the aligned firstliquid crystal, thereby forming a first retardation layer thatselectively reflects light whose wavelength falls in a range differentfrom the wave range of incident light.

[0028] According to the second feature of the present invention, it ispossible to obtain a retardation optical element that does not producebright and dark fringes on a displayed image and can effectively preventlowering of display quality.

[0029] In the method of producing a retardation optical elementaccording to the second feature of the present invention, it ispreferable that the thickness of the first liquid crystal that isapplied to the surface of the alignment layer be so adjusted that thedirections of the directors of the liquid crystalline molecules on thesurface of the two opposite main surfaces of the first retardationlayer, which surface is not controlled by the alignment regulation powerof the surface of the alignment layer, are regulated. If the thicknessof the first retardation layer is so adjusted, the appearance of brightand dark fringes is more effectively prevented, and the lowering ofdisplay quality can thus be prevented more surely.

[0030] Further, in the method of producing a retardation optical elementaccording to the second feature of the present invention, it ispreferable that another alignment layer be brought into contact with thesurface of the first liquid crystal applied to the surface of thealignment layer, the contacting surface being on the side apart from thealignment layer, in order to regulate the directions of the directors ofthe liquid crystalline molecules on the surface of the two opposite mainsurfaces of the retardation layer, which surface is not controlled bythe alignment regulation power of the surface of the alignment layer. Ifanother alignment layer is so provided, the appearance of bright anddark fringes is more effectively prevented, and the lowering of displayquality can thus be prevented more surely.

[0031] Preferably, the method of producing a retardation optical elementaccording to the second feature of the present invention furthercomprises the steps of: directly applying, to the first retardationlayer, a second liquid crystal comprising at least one type of otherpolymerizable monomer or oligomer molecules having cholestericregularity, thereby aligning the second liquid crystal by the alignmentregulation power of the surface of the first retardation layer; andthree-dimensionally crosslinking and solidifying the aligned secondliquid crystal, thereby forming a second retardation layer thatselectively reflects light whose wavelength falls in a range differentfrom the wave range of incident light. If the method further comprisesthese steps, a retardation optical element composed of multipleretardation layers laminated, capable of preventing the appearance ofbright and dark fringes on a displayed image and of effectivelypreventing lowering of display quality can simply be obtained withoutseparately providing an alignment layer between the first and secondretardation layers.

[0032] In the method of producing a retardation optical elementaccording to the second feature of the present invention, it ispreferable that, in at least one of the the step of forming the firstretardation layer and that of forming the second retardation layer, thethickness of the first or second liquid crystal that is applied to thesurface of the alignment layer or of the first retardation layer be soadjusted that the directions of the directors of the liquid crystallinemolecules on the surface of the two opposite main surfaces of the firstor second retardation layer, which surface is not controlled by thealignment regulation power of the surface of the alignment layer or ofthe first retardation layer, are regulated. By so adjusting thethickness, it is possible to prevent appearance of bright and darkfringes more effectively and thus to prevent lowering of display qualitymore surely.

[0033] In the method of producing a retardation optical elementaccording to the second feature of the present invention, it ispreferable that, in at least one of the step of forming the firstretardation layer and that of forming the second retardation layer,another alignment layer be brought into contact with the surface of thefirst or second liquid crystal applied to the surface of the alignmentlayer or of the first retardation layer, the surface being on the sideapart from the surface of the alignment layer or of the firstretardation layer, in order to regulate the directions of the directorsof the liquid crystalline molecules on the surface of the two oppositemain surfaces of the first or second retardation layer, which surface isnot controlled by the alignment regulation power of the surface of thealignment layer or of the first retardation layer. If another alignmentlayer is so provided, the appearance of bright and dark fringes isprevented more effectively, and the lowering of display quality can thusbe prevented more surely.

[0034] Further, in the method of producing a retardation optical elementaccording to the second feature of the present invention, it ispreferable that both of the first and second liquid crystals that areapplied to form the first and second retardation layers, respectively,have selective reflection wave ranges that are either shorter or longerthan the wave range of incident light. If the first and second liquidcrystals have such selective reflection wave ranges, material transferdoes not occur between the first and second retardation layers made fromthe first and second liquid crystals, respectively. It is thereforepossible to produce a retardation optical element as a more uniformlaminate of retardation layers and to more effectively control theoptical activity caused by the cholesteric-regular molecular structure.

[0035] Furthermore, in the method of producing a retardation opticalelement according to the second feature of the present invention, it ispreferable that the first and second liquid crystals that are applied toform the first and second retardation layers, respectively, comprisesubstantially the same material. If so, material transfer scarcelyoccurs between the first and second retardation layers made from thefirst and second liquid crystals, respectively, so that it is possibleto produce a retardation optical element as a more uniform laminate ofretardation layers.

[0036] A method of producing a retardation optical element according tothe third feature of the present invention comprises the steps of:applying a first liquid crystal comprising a liquid crystalline polymerhaving cholesteric regularity to an alignment layer that has been soformed that the surface thereof exerts alignment regulation power insubstantially one direction, thereby aligning the first liquid crystalby the alignment regulation power of the surface of the alignment layer;and solidifying the aligned first liquid crystal into a glassy state bycooling, thereby forming a first retardation layer that selectivelyreflects light whose wavelength falls in a range different from the waverange of incident light.

[0037] According to the third feature of the present invention, it ispossible to obtain a retardation optical element that produces no brightand dark fringes on a displayed image and can effectively preventlowering of display quality.

[0038] In the method of producing a retardation optical elementaccording to the third feature of the present invention, it ispreferable that the thickness of the first liquid crystal that isapplied to the surface of the alignment layer be so adjusted that thedirections of the directors of the liquid crystalline molecules on thesurface of the two opposite main surfaces of the first retardationlayer, which surface is not controlled by the alignment regulation powerof the surface of the alignment layer, are regulated. If the thicknessof the first liquid crystal is so adjusted, the appearance of bright anddark fringes is prevented more effectively, and the lowering of displayquality can thus be prevented more surely.

[0039] Further, in the method of producing a retardation optical elementaccording to the third feature of the present invention, it ispreferable that another alignment layer be brought into contact with thesurface of the first liquid crystal applied to the surface of thealignment layer, the contacting surface being on the side apart from thesurface of the alignment layer, in order to regulate the directions. ofthe directors of the liquid crystalline molecules on the surface of thetwo opposite main surfaces of the first retardation layer, which surfaceis not controlled by the alignment regulation power of the surface ofthe alignment layer. If another alignment layer is so provided, theappearance of bright and dark fringes is prevented more effectively, andthe lowering of display quality can thus be prevented more surely.

[0040] Furthermore, the method of producing a retardation opticalelement according to the third feature of the present invention furthercomprises the steps of: directly applying, to the first retardationlayer, a second liquid crystal comprising another liquid crystallinepolymer having cholesteric regularity, thereby aligning the secondliquid crystal by the alignment regulation power of the surface of thefirst retardation layer; and solidifying the aligned second liquidcrystal into a the glassy state by cooling, thereby forming a secondretardation layer that selectively reflects light whose wavelength fallsin a range different from the wave range of incident light. If themethod further comprises these steps, a retardation optical elementcomposed of multiple retardation layers laminated, capable of preventingappearance of bright and dark fringes on a displayed image and ofeffectively preventing lowering of display quality, can simply beobtained without separately providing an alignment layer between thefirst and second retardation layers.

[0041] In the method of producing a retardation optical elementaccording to the third feature of the present invention, it ispreferable that, in at least one of the step of forming the firstretardation layer and that of forming the second retardation layer, thethickness of the first or second liquid crystal that is applied to thesurface of the alignment layer or of the first retardation layer be soadjusted that the directions of the directors of the liquid crystallinemolecules on the surface of the two opposite main surfaces of the firstor second retardation layer, which surface is not controlled by thealignment regulation power of the surface of the alignment layer or ofthe first retardation layer, are regulated. By so adjusting thethickness of the first or second liquid crystal, it is possible toprevent appearance of bright and dark fringes more effectively and thusto prevent lowering of display quality more surely.

[0042] Further, in the method of producing a retardation optical elementaccording to the third feature of the present invention, it ispreferable that, in at least one of the step of forming the firstretardation layer and that of forming the second retardation layer,another alignment layer be brought into contact with the surface of thefirst or second liquid crystal applied to the surface of the alignmentlayer or of the first retardation layer, the contacting surface being onthe side apart from the surface of the alignment layer or of the firstretardation layer, in order to regulate the directions of the directorsof the liquid crystalline molecules on the surface of the two oppositemain surfaces of the first or second retardation layer, which surface isnot controlled by the alignment regulation power of the surface of thealignment layer or of the first retardation layer. If another alignmentlayer is so provided, the appearance of bright and dark fringes isprevented more effectively, and the lowering of display quality can thusbe prevented more surely.

[0043] Further, in the method of producing a retardation optical elementaccording to the third feature of the present invention, it ispreferable that both of the first and second liquid crystals that areapplied to form the first and second retardation layers, respectively,have selective reflection wave ranges that are either shorter or longerthan the wave range of incident light. If the first and the secondliquid crystals have such selective reflection wave ranges, materialtransfer does not occur between the first and second retardation layersmade from the first and second liquid crystals, respectively. It istherefore possible to produce a retardation optical element as a moreuniform laminate of retardation layers and to more effectively controlthe optical activity caused by the cholesteric-regular molecularstructure.

[0044] Furthermore, in the method of producing a retardation opticalelement according to the third feature of the present invention, it ispreferable that the first and second liquid crystals that are applied toform the first and second retardation layers, respectively, comprisesubstantially the same material. If so, material transfer scarcelyoccurs between the first and second retardation layers made from thefirst and second liquid crystals, respectively, so that it is possibleto produce a retardation optical element as a more uniform laminate ofretardation layers.

[0045] A polarization element according to the fourth feature of thepresent invention comprises: a polarizing layer; and a retardationoptical element according to the above-described first feature of thepresent invention, provided on the surface of the polarizing layer.

[0046] According to the fourth feature of the present invention, apolarizing layer is applied to at least one surface of the retardationoptical element by lamination or the like, so that the reflection oflight on the surface of the retardation optical element is drasticallydecreased. It is therefore possible to effectively prevent appearance ofbright and dark fringes and to improve contrast. The lowering of displayquality can thus be effectively prevented.

[0047] In the polarization element according to the fourth feature ofthe present invention, it is preferable that the directions of thedirectors of the liquid crystalline molecules on the one surface or theother surface of the retardation optical element be substantiallyparallel with or perpendicular to the axis of absorption of thepolarizing layer. By so controlling the directions of the directors ofthe liquid crystalline molecules, it is possible to more effectivelyprevent appearance of bright and dark fringes and to improve contrast.The lowering of display quality can thus be prevented more surely.

[0048] A liquid crystal display according to the fifth feature of thepresent invention comprises: a liquid crystal cell; a pair of polarizersso arranged that the liquid crystal cell is sandwiched therebetween; anda retardation optical element according to the above-described firstfeature of the present invention, placed between the liquid crystal celland at least one of the paired polarizers, wherein, of the light in apredetermined state of polarization, emerging from the liquid crystalcell, a part of the light that emerges slantingly in the directiondeviating from the normal of the liquid crystal cell is compensated bythe retardation optical element for the state of polarization.

[0049] According to the fifth feature of the present invention, theretardation optical element is arranged between the liquid crystal celland the polarizer in the liquid crystal display so that, of the lightemerging from the liquid crystal cell, a part of the light that emergesslantingly in the direction deviating from the normal of the liquidcrystal cell is compensated by the retardation optical element for thestate of polarization. It is therefore possible to prevent appearance ofbright and dark fringes on the liquid crystal display and to improvecontrast. The lowering of display quality can thus be prevented.

[0050] In the liquid crystal display according to the fifth feature ofthe present invention, it is preferable that the directions of thedirectors of the liquid crystalline molecules on the one surface or theother surface of the retardation optical element be substantiallyparallel with or perpendicular to the axis of absorption of each one ofthe polarizers. By so controlling the directions of the directors of theliquid crystalline molecules, it is possible to more effectively preventappearance of bright and dark fringes on the liquid crystal display andto improve contrast. The lowering of display quality can thus beprevented more surely.

BRIEF DESCRIPTION OF THE DRAWINGS

[0051] In the drawings,

[0052]FIG. 1 is an enlarged perspective view diagrammatically showing apart of a retardation optical element according to an embodiment of thepresent invention;

[0053]FIG. 2 is an enlarged perspective view diagrammatically showing apart of a modification of the retardation optical element according toan embodiment of the present invention;

[0054]FIGS. 3A, 3B and 3C are diagrammatic views showing therelationship between the helical pitch in the helical structureconsisting of liquid crystalline molecules, having cholestericregularity, and the directors of the liquid crystalline molecules on thesurfaces of a retardation layer;

[0055]FIG. 4 is a diagrammatic cross-sectional view illustrating a firstmethod of producing a retardation optical element according to anembodiment of the present invention;

[0056]FIG. 5 is a diagrammatic cross-sectional view illustrating amodification of the first method of producing a retardation opticalelement according to a embodiment of the present invention;

[0057]FIG. 6 is a diagrammatic cross-sectional view illustrating asecond method of producing a retardation optical element according to anembodiment of the present invention;

[0058]FIG. 7 is a diagrammatic cross-sectional view illustrating a firstmethod of producing a multi-layered retardation optical element that isincluded in the retardation optical element according to an embodimentof the present invention;

[0059]FIG. 8 is a diagrammatic view showing the directors of liquidcrystalline molecules on the two adjacent surfaces of each twoneighboring layers in a multi-layered retardation optical element thatis included in the retardation optical element according to anembodiment of the present invention;

[0060]FIG. 9 is a diagrammatic cross-sectional view illustrating asecond method of producing a multi-layered retardation optical elementthat is included in the retardation optical element according to anembodiment of the present invention;

[0061]FIG. 10 is a diagrammatic exploded perspective view of apolarization element including a retardation optical element accordingto an embodiment of the present invention;

[0062]FIG. 11 is a diagrammatic exploded perspective view of a liquidcrystal display including a retardation optical element according to anembodiment of the present invention;

[0063]FIG. 12 is a diagrammatic exploded perspective view showing adisposition in a case where a retardation optical element sandwichedbetween the polarizers is observed; and

[0064]FIG. 13 is a diagrammatic exploded perspective view of aconventional liquid crystal display.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0065] By referring to the accompanying drawings, embodiments of thepresent invention will be described hereinafter.

[0066] A retardation optical element according to this embodiment isfirstly described with reference to FIG. 1.

[0067] As shown in FIG. 1, this retardation optical element 10 includesa retardation layer 12 having a cholesteric-regular molecular structure(helical structure) with liquid crystalline molecules in planarorientation.

[0068] The retardation layer 12 with a cholesteric-regular molecularstructure has a rotated-light-selecting property(polarized-light-separating property) of separating a componentoptically rotated (circularly polarized) in one direction from acomponent optically rotated in the opposite direction according to thephysical orientation of the liquid crystalline molecules (planarorientation). This phenomenon is known as “circular dichroism.” If thedirection of rotation of the liquid crystalline molecules constitutingthe helical structure is properly selected, the component circularlypolarized in the same direction as this direction of rotation isselectively reflected.

[0069] In this case, the scattering of polarized light becomes maximum(the selective reflection is peaked) at the wavelength λ0 given by thefollowing equation (1):

[0070] λ0=nav·p,  (1)

[0071] wherein p is the helical pitch in the helical structureconsisting of liquid crystalline molecules, and nav is the meanrefractive index of a plane perpendicular to the helical axis.

[0072] On the other hand, the width Δλ of the wave range in which thewavelength of selectively reflected light falls is given by thefollowing equation (2):

Δλ=Δn·p,  (2)

[0073] wherein Δn is the birefringence, which is a difference betweenthe index of refraction for ordinary light and that of refraction forextraordinary light.

[0074] Namely, with respect to non-polarized light incident on theretardation layer 12 having such a cholesteric-regular molecularstructure, either right-handed or left-handed circularly polarizedcomponent of light in a selective reflection wave range with a centralwavelength λ0 and a width Δλ is reflected owing to the above-describedpolarized-light-separating property, and the other circularly polarizedcomponent of the light and light (non-polarized light) not in thisselective reflection wave range are transmitted. It is noted that theright-handed or left-handed circularly polarized component is reflectedwithout undergoing reversion of the direction of rotation unlike in thecase of ordinary reflection of light.

[0075] The helical pitch in the molecular structure of the retardationlayer 12 is herein so adjusted that the retardation layer 12 selectivelyreflects, owing to its molecule structure, light whose wavelength fallsin a range that is different from the wave range of light incident onthe retardation layer 12 (a selective reflection wave range that isshorter or longer than the wave range of the incident light).

[0076] The purpose of making the selective reflection wave range of theretardation layer 12 either shorter or longer than the wave range of theincident light is to prevent selective reflection of the incident lightthat can occur owing to the cholesteric-regular molecular structure.Therefore, in the case where the light incident on the retardation layer12 is visible light (wave range: 380-780 nm), the wavelength of thelight selectively reflected by the retardation layer 12 owing to itscholesteric-regular molecular structure is preferably 380 nm or less or780 nm or more. As long as the wavelength of the selectively reflectedlight falls in this range, it is possible to avoid the coloring problemand the like that are brought about by the reflection of visible light,while letting the retardation layer 12 function as a negative C plate.That the wave range of the selectively reflected light is shorter thanthe wave range of the incident light is more preferred because, in thiscase, the optical activity is smaller.

[0077] Further, the retardation layer 12 has two opposite main surfaces(surfaces with larger areas) 12A and 12B that are perpendicular to eachother in the direction of thickness, as shown in FIG. 1.

[0078] The directions of the directors Da of the liquid crystallinemolecules on the entire area of the surface 12A, one of the two mainsurfaces 12A and 12B, are substantially the same, and, at the same time,the directions of the directors Db of the liquid crystalline moleculeson the entire area of the other surface 12B are also substantially thesame. The dispersion in the directions of the directors of the liquidcrystalline molecules on each of the one surface 12A and the othersurface 12B of the retardation layer 12 is within ±10°, preferablywithin ±5°, more preferably ±1°.

[0079] The expression “substantially the same” as used hereinencompasses the case where the directions of the directors of the liquidcrystalline molecules are different by an angle of approximately 180°,that is, the head of a liquid crystalline molecule and the tail ofanother one are in the same direction. This is because, in many cases,the head of a liquid crystalline molecule is optically indistinguishablefrom its tail. The same is true for the case that will be describedlater (the case where the directions of the directors Da and Db of theliquid crystalline molecules on the surfaces 12A and 12B of theretardation layer 12 are substantially parallel with each other).

[0080] Whether the directions of the directors Da and Db of the liquidcrystalline molecules on the surfaces 12A and 12B are substantially thesame or not can be known by observing the cross section of theretardation layer 12 by a transmission electron microscope.Specifically, when the cross section of the retardation layer 12 thathas been solidified with its cholesteric-regular molecular structuremaintained is observed by a transmission electron microscope, bright anddark fringes are observed correspondingly to the pitches of themolecular helixes characteristic of the cholesteric-regular molecularstructure. Therefore, if the bright and dark fringes that appear on eachsurface 12A and 12B are seen almost the same in terms of concentration,it can be judged that the directions of the directors of the liquidcrystalline molecules on this surface are substantially the same.

[0081] The term “liquid crystalline molecules” is usually used toindicate those molecules that have both the fluidity of liquid and theanisotropy of crystal. However, in this specification, this term “liquidcrystalline molecules” is also used, for convenience' sake, to indicatethose molecules that have been solidified while retaining anisotropywhich the molecules possessed when they are in the fluid state. Examplesof methods of solidifying molecules while retaining anisotropy which themolecules possessed when they are in the fluid state include the methodin which liquid crystalline molecules having polymerizable groups(polymerizable monomer or oligomer molecules) are crosslinked, and themethod in which a high-molecular-weight liquid crystal (liquidcrystalline polymer) is cooled to a temperature below its glasstransition temperature.

[0082] The retardation layer 12 having the above-describedcholesteric-regular molecular structure has anisotropy, that is, doublerefractivity, and its refractive index in the direction of thickness isdifferent from that in the direction of plane. The retardation layer 12therefore functions as a negative C plate.

[0083] Namely, in the three-dimensional rectangular coordinates, when Nxand Ny represent the refractive indexes of the retardation layer 12 inthe direction of plane, and Nz, that of the retardation layer 12 in thedirection of thickness, these Nx, Ny and Nz are in the relationshipNz<Nx=Ny. For this reason, although linearly polarized light that entersthe retardation layer 12 along its normal 12C is transmitted withoutundergoing phase shift, linearly polarized light that slantingly entersthe retardation layer 12 in the direction deviating from the normal 12Cundergoes phase shift to become elliptically polarized light. It is alsopossible, on the contrary, to convert elliptically polarized light thatslantingly enters the retardation layer 12 in the direction deviatingfrom the normal 12C into linearly polarized light.

[0084] In the retardation layer 12 included in the retardation opticalelement 10 according to the above-described embodiment, the directionsof the directors Da and Db of the liquid crystalline molecules on theentire areas of the main surfaces 12A and 12B are substantially thesame, respectively. However, in the case where the retardation layer 12are divided into multiple sections, it is enough to make the directionsof the directors Da and Db of the liquid crystalline molecules in eachsection of the main surfaces 12A and 12B substantially the same,respectively.

[0085] Next, a modification of the retardation optical element accordingto this embodiment will be described with reference to FIG. 2.

[0086] As shown in FIG. 2, this retardation optical element 20 includesa retardation layer 22 having a cholesteric-regular molecular structure(helical structure) with liquid crystalline molecules in planarorientation.

[0087] The retardation layer 22 has two opposite main surfaces (surfaceswith larger areas) 22A and 22B that are perpendicular to each other inthe direction of thickness, as shown in FIG. 2.

[0088] The directions of the directors Da of the liquid crystallinemolecules on the entire area of the surface 22A, one of the two mainsurfaces 22A and 22B, are substantially the same, and, at the same time,the directions of the directors Db of the liquid crystalline moleculeson the entire area of the other surface 22B are also substantially thesame. The dispersion in the directions of the directors of the liquidcrystalline molecules on each of the one surface 22A and the othersurface 22B of the retardation layer 22 is within ±10°, preferablywithin ±5°, more preferably ±1°.

[0089] Further, it is preferable that the directions of the directors Daof the liquid crystalline molecules on the one surface 22A of theretardation layer 22 be substantially parallel with those of thedirectors Db of the liquid crystalline molecules on the other surface22B of the retardation layer 22. The angle made by the directions (meandirection) of the directors of the liquid crystalline molecules on theone surface 22A of the retardation layer 22 and the directions (meandirection) of the directors of the liquid crystalline molecules on theother surface 22B of the retardation layer 22 is within ±10°, preferablywithin ±5°, more preferably ±1°.

[0090] The other details about the construction of the retardation layer22 in the retardation optical element 20 are basically the same as thoseabout the construction of the aforementioned retardation layer 12 in theretardation optical element 10, so that detailed descriptions for themare herein omitted.

[0091] In the retardation optical element 20, it is preferable to makethe thickness of the retardation layer 22 equal to (0.5×integer) timesthe helical pitch p in the helical structure consisting of liquidcrystalline molecules, in order to make the directions of the directorsDa and Db of the liquid crystalline molecules on the two oppositesurfaces 22A and 22B agree with each other with high accuracy. If thethickness of the retardation layer 22 is so made, it can optically bedivided, without a remainder, by a half of the helical pitch p in thehelical structure consisting of liquid crystalline molecules, asdiagrammatically shown in FIGS. 3A, 3B and 3C, for example. There canthus be avoided optical deviation from the above equation (1), which isa simplified theoretical equation, especially disturbance of the stateof polarization that is caused by phase shift that occurs for the lightentering along the helical axis.

[0092] Also in the above case, the angle made by the directions of thedirectors Da of the liquid crystalline molecules on the one surface 22Aof the retardation layer 22 and those of the directors Db of the liquidcrystalline molecules on the other surface 22B of the retardation layer22 is within ±10°, preferably within ±5°, more preferably ±1°.

[0093] In the retardation layer 22 included in the retardation opticalelement 20 according to the above-described embodiment, the directionsof the directors Da and Db of the liquid crystalline molecules on theentire areas of the main surfaces 22A and 22B are substantially thesame, respectively, and, at the same time, the directions of thedirectors Da of the liquid crystalline molecules on the one surface 22Aare substantially parallel with those of the directors Db of the liquidcrystalline molecules on the other surface 22B. However, in the casewhere the retardation layer 22 is divided into multiple sections, it isenough to make the directions of the directors Da and Db of the liquidcrystalline molecules in each section of the main surfaces 22A and 22Bsubstantially the same, respectively, and to make the directions of thedirectors Da of the liquid crystalline molecules in each section of theone surface 22A substantially parallel with those of the directors Db ofthe liquid crystalline molecules on the corresponding section of theother surface 22B.

[0094] Useful as materials for the retardation layers 12 and 22 in theretardation optical elements 10 and 20 are three-dimensionallycrosslinkable liquid crystalline monomers or oligomers (polymerizablemonomer or oligomer molecules), as well as high-molecular-weight liquidcrystals (liquid crystalline polymers) that can be solidified into aglassy state by cooling.

[0095] In the case where the retardation layers 12 and 22 are made fromthree-dimensionally crosslinkable, polymerizable monomer molecules, itis possible to use mixtures of liquid crystalline monomers and chiralcompounds as disclosed in Japanese Laid-Open Patent Publication No.258638/1995 and Published Japanese Translation No. 508882/1998 of PCTInternational Publication for Patent Application. If three-dimensionallycrosslinkable, polymerizable oligomers are used, it is desirable to usecyclic organopolysiloxane compounds and the like having cholestericphases as disclosed in Japanese Laid-Open Patent Publication No.165480/1982. By “three-dimensional crosslinking” is herein meant thatpolymerizable monomer or oligomer molecules are three-dimensionallypolymerized to give a network structure. By making the molecules intosuch a state, it is possible to optically fix the liquid crystallinemolecules while retaining its cholesteric liquid crystalline state andthus to obtain a film that is easy to handle as an optical film andstable at normal temperatures.

[0096] Taken herein as an example is the case where three-dimensionallycrosslinkable, polymerizable monomer molecules are used. In this case, achiral nematic liquid crystal (cholesteric liquid crystal) can beobtained by adding a chiral agent to a liquid crystalline monomer havingnematic liquid crystal phase. More specifically, it is possible to useliquid crystalline monomers represented by the general formulae (1) to(11), for example. In liquid crystalline monomers represented by thegeneral formula (11), X is preferably an integer of 2 to 5.

[0097] (Formulae (1) to (11))

[0098] It is preferable to use, as the chiral agent, those compoundsrepresented by the general formulae (12) to (14), for example. In chiralagents having the general formula (12) or (13), X is preferably aninteger of 2 to 12. In chiral agents having the general formula (14), Xis preferably an integer of 2 to 5. R⁴ in the general formula (12)represents hydrogen or methyl group. (Formulae (12) to (14))

[0099] On the other hand, in the case where the retardation layers 12and 22 are made from liquid crystalline polymers, there can be used:polymers containing mesogen groups, which make the polymers liquidcrystalline, in their main or side chains, or in both their main andside chains; high-molecular-weight cholesteric liquid crystals havingcholesteryl groups in their side chains; liquid crystalline polymers asdisclosed in Japanese Laid-Open Patent Publication No. 133810/1997,liquid crystalline polymers as disclosed in Japanese Laid-Open PatentPublication No. 293252/1999, and so forth.

[0100] Next, methods of producing the retardation optical elements 10and 20 having the above constructions according to the aforementionedembodiments will be described hereinafter.

[0101] (First Production Method)

[0102] Firstly, a production method that is employed when polymerizablemonomer or oligomer molecules are used as a material for a retardationlayer will be described with reference to FIGS. 4(A) to 4(C).

[0103] In this production method, an alignment layer 16 is formed, inadvance, on a glass substrate or a polymeric film 14 such as a TAC(cellulose triacetate) film, as shown in FIG. 4(A). To this alignmentlayer 16, polymerizable monomer molecules (or polymerizable oligomermolecules) 18 are applied as the liquid crystalline molecules, as shownin FIG. 4(B), and are aligned by the alignment regulation power of thealignment layer 16. At this time, the applied polymerizable monomermolecules (or polymerizable oligomer molecules) 18 form a liquid crystallayer.

[0104] Next, while retaining this state of alignment, polymerization ofthe polymerizable monomer molecules (or polymerizable oligomermolecules) 18 is initiated by the combination use of aphotopolymerization initiator previously added and ultraviolet lightexternally applied, or is directly initiated by the application of anelectron beam, as shown in FIG. 4(C), thereby three-dimensionallycrosslinking (polymerizing) and solidifying the polymerizable monomermolecules (or polymerizable oligomer molecules) 18. Thus, there isobtained a retardation optical element 10 including the above-describedsingle retardation layer 12, functioning as a negative C plate.

[0105] If the alignment layer 16 has been so formed that its entiresurface exerts alignment regulation power in substantially onedirection, the directions of the directors Da of the liquid crystallinemolecules that are in contact with the alignment layer 16 becomesubstantially the same over the contact face.

[0106] In this case, to make the directions of the directors Db of theliquid crystalline molecules on the surface 12B that is on the sideapart from the alignment layer 16 substantially the same over the entirearea of the surface 12B, as shown in FIG. 1, it is enough to make thethickness of the retardation layer 12 uniform. Further, in a series ofthe steps shown in FIGS. 4(A) to 4(C), the following step may beeffected as shown in FIGS. 5(A) to 5(D) after applying the polymerizablemonomer molecules (or polymerizable oligomer molecules) 18 to thealignment layer 16 and before three-dimensionally crosslinking thesemolecules: a second alignment layer 16A is superposed on the appliedpolymerizable monomer molecules (polymerizable oligomer molecules) 18(FIG. 5(C)), and these molecules sandwiched between the alignment layer16 and the second alignment layer 16A are three-dimensionallycrosslinked by the application of ultraviolet light or an electron beam(FIG. 5(D)), like in the step shown in FIG. 4(C). The second alignmentlayer 16A may be separated from the retardation layer 12 after theapplication of ultraviolet light or an electron beam.

[0107] In order to decrease the viscosity of the polymerizable monomermolecules (or polymerizable oligomer molecules) 18 so that they can beapplied with ease, they may be dissolved in a solvent to obtain acoating liquid. If such a coating liquid is used, it is necessary toeffect the drying step of evaporating the solvent before the step ofthree-dimensionally crosslinking the polymerizable monomer molecules (orpolymerizable oligomer molecules) 18 by the application of ultravioletlight or an electron beam. Preferably, after effecting the step ofapplying the coating liquid, the drying step is effected to evaporatethe solvent, and the alignment step is then effected to align the liquidcrystal.

[0108] Further, if the polymerizable monomer molecules (or polymerizableoligomer molecules) 18 are made into a liquid crystal layer at apredetermined temperature, the resulting liquid crystal layer isnematic. If any chiral agent is added to this nematic liquid crystallayer, a chiral nematic liquid crystalline phase (cholesteric liquidcrystalline phase) is developed. Specifically, it is enough to add achiral agent to the polymerizable monomer or oligomer molecules in anamount of several to 10%. By varying the chiral power by changing thetype of the chiral agent to be added, or by changing the concentrationof the chiral agent in the polymerizable monomer or oligomer molecules,it is possible to control the selective reflection wave range, which isdetermined by the molecular structure consisting of the polymerizablemonomer or oligomer molecules.

[0109] The alignment layer 16 and/or the second alignment layer 16A canbe formed by a conventionally known method. For example, the alignmentlayer may be formed by the method in which a PI (polyimide) or PVA(polyvinyl alcohol) film is formed on the above-described glasssubstrate or polymeric film 14 such as a TAC film and is then rubbed, orthe method in which a polymeric compound film that can serve as anoptical alignment layer is formed on a glass substrate or a polymericfilm 14 such as a TAC film and is irradiated with polarized UV(ultraviolet light). Moreover, oriented PET (polyethylene terephthalate)films, etc. can also be used for the alignment layer 16 and/or thesecond alignment layer 16A.

[0110] In the case where a polymeric film such as a TAC film is used asa substrate on which the alignment layer 16 is formed, it is preferableto previously provide a barrier layer on the polymeric film so that thesubstrate is not damaged by a solvent in which the polymerizable monomermolecules (or polymerizable oligomer molecules) 18 are dissolved toobtain a coating liquid; the coating liquid is then applied to thisbarrier layer.

[0111] On the other hand, when the retardation optical element 20 asshown in FIG. 2 is produced, the thickness of the retardation layer 22is made uniform and equal to (0.5×integer) times the helical pitch p inthe helical structure consisting of the liquid crystalline molecules. Inthis case, it is possible to employ not only the method in which thethickness of the retardation layer 22 is adjusted, but also the methodin which the above-described second alignment layer 16A is employed,where the direction in which the second alignment layer 16A exerts itsalignment regulation power is made the same as the direction in whichthe alignment layer 16 exerts its alignment regulation power.

[0112] In the retardation optical elements 10 and 20 produced in theabove-described manners, if the second alignment layer 16A is used inaddition to the alignment layer 16 in order to make the directions ofthe directors Da and Db of the liquid crystalline molecules on thesurfaces 12A, 12B, 22A and 22B of the retardation layers 12 and 22substantially the same over the entire areas of the surfaces 12A, 12B,22A and 22B, respectively, the first alignment layer 16 and the secondalignment layer 16A regulate the directions of the directors Da and Dbof the liquid crystalline molecules on the surfaces 12A, 12B, 22A and22B of the retardation layers 12 and 22, respectively. Therefore, it isnot necessary that the thickness of the retardation layers 12 and 22 behighly uniform as required in the case where the second alignment layer16A is not used. Namely, as long as the directions of the directors Daand Db of the liquid crystalline molecules on the surfaces 12A, 12B, 22Aand 22B of the retardation layers 12 and 22 are substantially the sameover the entire areas of the surfaces 12A, 12B, 22A and 22B,respectively, it is not necessary that the helical pitches p in thehelical structures of the retardation layers 12 and 22 be constant inplanes extending in parallel with the surfaces 12A, 12B, 22A and 22B ofthe retardation layers 12 and 22, respectively, and they may varyaccording to changes in film thickness. Similarly, it is not necessarythat the pitch numbers in the helical structures of the retardationlayers 12 and 22 be constant in planes extending in parallel with thesurfaces 12A, 12B, 22A and 22B, and they may vary according to changesin film thickness.

[0113] (Second Production Method)

[0114] Next, a production method that is employed when a liquidcrystalline polymer is used as a material for a retardation layer willbe described with reference to FIGS. 6(A) to 6(C).

[0115] In this production method, an alignment layer 16 is previouslyformed on a glass substrate or a polymeric film 14 such as a TAC film,as shown in FIG. 6(A), like in the above-described production method.

[0116] Next, a liquid crystalline polymer 34 having cholestericregularity is applied to the alignment layer 16, as shown in FIG. 6(B),and is thus aligned by the alignment regulation power of the alignmentlayer 16. At this time, the applied liquid crystalline polymer 34 formsa liquid crystal layer.

[0117] Thereafter, the liquid crystalline polymer 34 is cooled to atemperature below its glass transition temperature (Tg) to make it intoa glassy state, as shown in FIG. 6(C). There is thus obtained aretardation optical element 30 composed of a single retardation layer32.

[0118] In this production method, in order to decrease the viscosity ofthe liquid crystalline polymer 34 so that it can be applied with ease,it may be dissolved in a solvent to obtain a coating liquid. If such acoating liquid is used, it is necessary to effect, before the coolingstep, the drying step of evaporating the solvent. Preferably, aftereffecting the step of applying the coating liquid, the drying step iseffected to evaporate the solvent, and the alignment step is theneffected to align the liquid crystal.

[0119] Further, in the case where a polymeric film such as a TAC film isused as a substrate on which the alignment layer 16 is formed, it ispreferable to previously provide a barrier layer on the polymeric filmso that the substrate is not damaged by the solvent in which the liquidcrystalline polymer 34 is dissolved to obtain the coating liquid; thecoating liquid is then applied to this barrier layer.

[0120] Cholesteric liquid crystalline polymers having chiral power inthemselves, as well as mixtures of nematic liquid crystalline polymersand cholesteric liquid crystalline polymers may be used as the liquidcrystalline polymer 34.

[0121] The state of such a liquid crystalline polymer 34 changes withtemperature. For example, a liquid crystalline polymer 34 having a glasstransition temperature of 90° C. and an isotropic transition temperatureof 200° C. remains in the state of cholesteric liquid crystal at atemperature between 90° C. and 200° C.; when this polymer is cooled toroom temperature, it is solidified into a glassy state with itscholesteric structure maintained.

[0122] To control the wavelength of incident light that is selectivelyreflected by the liquid crystalline polymer 34 owing to itscholesteric-regular molecular structure, the chiral power in the liquidcrystalline molecules may be controlled by a conventional method if acholesteric liquid crystalline polymer is used as the liquid crystallinepolymer 34. If a mixture of a nematic liquid crystalline polymer and acholesteric liquid crystalline polymer is used, it is possible tocontrol the selective reflection wavelength by adjusting the mixingratio of these two components.

[0123] Also in the above-described production method, if the alignmentlayer 16 has been so formed that its entire surface exerts alignmentregulation power in substantially one direction, the directions of thedirectors of the liquid crystalline molecules on the one surface 12A ofthe retardation layer 12 that is in contact with the alignment layer 16can be made substantially the same over the contact face.

[0124] To make the directors Db of the liquid crystalline molecules onthe surface 12B that is on the side apart from the alignment layer 16substantially the same over the entire area of the surface 12B, thethickness of the retardation layer 12 may be made uniform, or a secondalignment layer 16A as shown in FIGS. 5(C) and 5 (D) may be provided onthe surface of the liquid crystalline polymer 34 that is on the sideapart from the first alignment layer 16.

[0125] Further, to make the directions of the directors of the liquidcrystalline molecules on the surface of the retardation layer 32 that ison the side opposite to the alignment layer 16 agree with the directionin which the alignment layer 16 exerts its alignment regulation power(that is, the directions of the directors of the liquid crystallinemolecules on the surface of the liquid crystal layer that is in contactwith the alignment layer 16), the thickness of the liquid crystal to beapplied may be adjusted like in the above-described case so that thethickness of the retardation layer 32 is equal to (0.5×integer) timesthe helical pitch p in the helical structure consisting of the liquidcrystalline molecules, or a second alignment layer 16A as shown in FIGS.5(C) and 5(D) may be employed. In the case where a second alignmentlayer 16A is employed, this layer is brought into contact with thesurface of the liquid crystalline polymer 34 that is on the side apartfrom the first alignment layer 16 so that the direction in which thesecond alignment layer 16A exerts its alignment regulation power agreeswith that in which the alignment layer 16 exerts its alignmentregulation power.

[0126] In the case where a second alignment layer 16A is used inaddition to the alignment layer 16 in order to make the directions ofthe directors Da and Db, of the liquid crystalline molecules on thesurfaces 32A and 32B of the retardation layer 32 substantially the sameover the entire areas of the surfaces 32A and 32B, respectively, thedirections of the directors of the liquid crystalline molecules on thesurfaces 32A and 32B of the retardation layer 32 are regulated by thefirst alignment layer 16 and the second alignment layer 16A,respectively. Therefore, it is not necessary that the thickness of theretardation layer 32 be highly uniform as required in the case where asecond alignment layer 16A is not used. Namely, as long as thedirections of the directors Da and Db of the liquid crystallinemolecules on the surfaces 32A and 32B of the retardation layer 32 aresubstantially the same over the entire areas of the surfaces 32A and32B, respectively, it is not necessary that the helical pitch p in thehelical structure of the retardation layer 32 be constant in planesextending in parallel with the surfaces 32A and 32B of the retardationlayer 32, and the helical pitch p may vary according to changes in filmthickness. Similarly, it is not necessary that the pitch number in thehelical structure of the retardation layer 32 be constant in planesextending in parallel with the surfaces 32A and 32B, and it may varyaccording to changes in film thickness.

[0127] Each of the retardation optical elements 10, 20 and 30 accordingto the aforementioned embodiments is composed of a single retardationlayer. The embodiments of the invention are not limited to this, andmulti-layered retardation optical elements are also acceptable.

[0128] Specifically, like a retardation optical element 40 as shown inFIG. 7(E), multiple retardation layers 42 and 44, each having acholesteric-regular molecular structure with liquid crystallinemolecules in planar orientation, may successively, directly belaminated. In such a multi-layered retardation optical element 40, ifthose layers that are different in birefringence, helical pitch, or thelike are used as the retardation layers 42 and 44, it becomes possibleto attain various types of optical compensations.

[0129] In this multi-layered retardation optical element 40, thedirections of the directors of the liquid crystalline molecules aresubstantially the same over the entire areas of the two opposite,outermost, main surfaces of the laminate of the liquid crystal layers 42and 44, respectively, as shown in FIG. 1. Further, it is preferable thatthe directions of the directors of the liquid crystalline molecules onone of the two opposite, outermost, main surfaces of the laminate of theliquid crystal layers 42 and 44 be substantially parallel with those ofthe directors of the liquid crystalline molecules on the other surfaceof the laminate. Furthermore, it is preferable that the directions ofthe directors of the liquid crystalline molecules in the vicinity of theinterface of the two neighboring liquid crystal layers 42 and 44 besubstantially parallel with each other.

[0130] A method of producing a multi-layered retardation optical elementwill be described hereinafter.

[0131] (First Production Method)

[0132] A production method that is employed in the case wherepolymerizable monomer or oligomer molecules are used as materials forretardation layers is described with reference to FIGS. 7(A) to 7(E).

[0133] In this production method, an alignment layer 16 is formed, inadvance, on a glass substrate or a polymeric film 14 such as a TAC film,as shown in FIG. 7(A). To this alignment layer 16, polymerizable monomermolecules (or polymerizable oligomer molecules) 18 are applied as liquidcrystalline monomers, as shown in FIG. 7(B), and are thus aligned by thealignment regulation power of the alignment layer 16.

[0134] Next, while retaining this state of alignment, the polymerizablemonomer molecules (polymerizable oligomer molecules) 18 arethree-dimensionally crosslinked and solidified, as described above, bythe combination use of a photopolymerization initiator and ultravioletlight, or by the application of an electron beam alone, thereby forminga first retardation layer 42.

[0135] To this three-dimensionally crosslinked first retardation layer42, another polymerizable monomer molecules (polymerizable oligomermolecules) 19 separately prepared are directly applied as shown in FIG.7(D), and are aligned, as shown in FIG. 8, by the alignment regulationpower of the surface of the three-dimensionally crosslinked firstretardation layer 42. While retaining this state of alignment, thepolymerizable monomer molecules (polymerizable oligomer molecules) 19are three-dimensionally crosslinked and solidified, as described above,by the combination use of a photopolymerization initiator andultraviolet light, or by the application of an electron beam alone, asshown in FIG. 7(E), thereby forming a second retardation layer 44. Thereis thus produced a two-layered retardation optical element 40.

[0136] To obtain a multi-layered retardation optical element composed ofthree or more retardation layers, the above-described steps (FIGS. 7(D)and 7(E)) are repeatedly effected to successively laminate a requirednumber of retardation layers.

[0137] In order to decrease the viscosity of the polymerizable monomermolecules (polymerizable oligomer molecules) 18 and 19 so that they canbe applied with ease, these molecules may be dissolved in solvents toobtain coating liquids. If such coating liquids are used, it isnecessary to effect the drying step to evaporate the solvents beforethree-dimensionally crosslinking the polymerizable monomer molecules(polymerizable oligomer molecules) 18 and 19 by the application ofultraviolet light or an electron beam. Preferably, after effecting thestep of applying the coating liquid, the drying step is effected toevaporate the solvent, and the alignment step is then effected to alignthe liquid crystal.

[0138] Also in this production method, if the alignment layer 16 hasbeen so formed that its entire surface exerts alignment regulation powerin substantially one direction, the directions of the directors of theliquid crystalline molecules that are brought into contact with thealignment layer 16 become substantially the same over the contact face.

[0139] To make the directions of the directors of the liquid crystallinemolecules on the surface on the side apart from the alignment layer 16substantially the same over the entire area of this surface, it isenough to make the thickness of the retardation layers 42 and 44uniform. Alternatively, when the first retardation layer 42 isthree-dimensionally crosslinked and solidified, a second alignment layer16A as shown in FIGS. 5(C) and 5(D) may be provided on the surface ofthe polymerizable monomer molecules (polymerizable oligomer molecules)18 that is on the side apart from the surface of the first alignmentlayer 16. Similarly, when the second retardation layer 44 isthree-dimensionally crosslinked and solidified, a second alignment layermay be provided on the surface of the polymerizable monomer molecules(polymerizable oligomer molecules) 19 that is on the side apart from thesurface of the first retardation layer 42. In the production of amulti-layered retardation optical element composed of three or moreretardation layers, the above steps may be effected for the third andlater retardation layers.

[0140] Further, to make the directions of the directors of the liquidcrystalline molecules on the surface of the first retardation layer 42that is on the side opposite to the alignment layer 16 agree with thedirection in which the alignment layer 16 exerts its alignmentregulation power (i.e., the directions of the directors of the liquidcrystalline molecules on the surface of the liquid crystal layer that isin contact with the alignment layer 16), or to make the directions ofthe directors of the liquid crystalline molecules on the surface of thesecond retardation layer 44 that is on the side opposite to the surfaceof the first retardation layer 42 agree with the direction in which thefirst retardation layer 42 exerts its alignment regulation power, thethickness of the liquid crystals to be applied may be adjusted so thatthe thickness of the first retardation layer 42 and that of the secondretardation layer 44 are respectively equal to (0.5×integer) times thehelical pitch p in the helical structure consisting of the liquidcrystalline molecules, or a second alignment layer 16A as shown in FIGS.5(C) and 5(D) may be employed. In the case where a second alignmentlayer 16A is employed, this layer is brought into contact with thesurface of the first retardation layer 42 that is on the side oppositeto the alignment layer 16, or with the surface of the second retardationlayer 44 facing the surface of the first retardation layer 42.

[0141] It is herein preferable that both of the liquid crystals that areapplied to form the first retardation layer 42 and the secondretardation layer 44 have selective reflection wave ranges that areshorter than the wave range of incident light. If the liquid crystalshave such selective reflection wave ranges, material transfer does notoccur between the first retardation layer 42 and the second retardationlayer 44 respectively formed by the application of the liquid crystals.It is therefore possible to produce a retardation optical element 40 asa more uniform laminate of retardation layers and to more effectivelycontrol the optical activity caused by the cholesteric-regular molecularstructure. In some cases, both of the liquid crystals that are appliedto form the first retardation layer 42 and the second retardation layer44 can have selective reflection wave ranges longer than the wave rangeof incident light.

[0142] Preferably, the liquid crystals that are applied to form thefirst retardation layer 42 and the second retardation layer 44 aresubstantially the same material. If so, material transfer scarcelyoccurs between the first retardation layer 42 and the second retardationlayer 44 respectively formed by the application of the liquid crystals.It is therefore possible to produce a retardation optical element 40 asa more uniform laminate of retardation layers.

[0143] (Second Production Method)

[0144] A production method that is employed when liquid crystallinepolymers are used as materials for retardation layers will be describedhereinafter with reference to FIGS. 9(A) to 9(C).

[0145] In this production method, an alignment layer 16 is formed, inadvance, on a glass substrate or a polymeric film 14 such as a TAC film,as shown in FIG. 9(A), like in the above-described production method.

[0146] Next, a liquid crystalline polymer having cholesteric regularityis applied to the alignment layer 16, as shown in FIG. 9(B), and is thusaligned by the alignment regulation power of the alignment layer 16.This liquid crystalline polymer is cooled to a temperature below itsglass transition temperature (Tg) to make it into a glassy state,thereby forming a first liquid crystal layer 42′.

[0147] Thereafter to this first liquid crystal layer 42′, another liquidcrystalline polymer having cholesteric regularity, separately prepared,is directly applied, and is aligned by the alignment regulation power ofthe surface of the first liquid crystal layer 42′ that has been madeinto a glassy state. This liquid crystalline polymer is cooled to atemperature below its glass transition temperature (Tg) to make it intoa glassy state, as described above, thereby forming a second liquidcrystal layer 44′. There is thus obtained a two-layered retardationoptical element 40′ including the second liquid crystal layer 44′.

[0148] The above-described step (FIG. 9(C)) is repeatedly effected toobtain a multi-layered retardation optical element composed of three ormore retardation layers.

[0149] Also in the above-described production method, if the alignmentlayer 16 has been so formed that its entire surface exerts its alignmentregulation power in substantially one direction, the directions of thedirectors of the liquid crystalline molecules that are brought intocontact with the alignment layer 16 become substantially the same overthe contact face.

[0150] To make the directors of the liquid crystalline molecules on thesurface on the side apart from the alignment layer 16 substantially thesame over the entire area of this surface, the thickness of theretardation layers 42′ and 44′ may be made uniform, or a secondalignment layer 16A as shown in FIGS. 5(C) and 5(D) may be provided onthe surface of the polymerizable monomer molecules (polymerizableoligomer molecules) 18 that is on the side apart from the surface of thefirst alignment layer 16, when the first retardation layer 42′ isthree-dimensionally crosslinked and solidified. Similarly, when thesecond retardation layer 44′ is three-dimensionally crosslinked andsolidified, a second alignment layer may be provided on the surface ofthe polymerizable monomer molecules (polymerizable oligomer molecules)19 that is on the side apart from the surface of the first retardationlayer 42′. In the production of a multi-layered retardation opticalelement composed of three or more retardation layers, these steps may beeffected for the third and later retardation layers.

[0151] Further, to make the directions of the directors of the liquidcrystalline molecules on the surface of the first retardation layer 42′that is on the side opposite to the alignment layer 16 agree with thedirection in which the alignment layer 16 exerts its alignmentregulation power (that is, the directions of the directors of the liquidcrystalline molecules on the surface of the liquid crystal layer that isin contact with the alignment layer 16), and to make the directions ofthe directors of the liquid crystalline molecules on the surface of thesecond retardation layer 44′ that is on the side opposite to the surfaceof the first retardation layer 42′ agree with the direction in which thefirst retardation layer 42′ exerts its alignment regulation power, thethickness of the liquid crystal layers to be applied is adjusted like inthe above-described production method so that the thickness of the firstretardation layer 42′ and that of the second retardation layer 44′ arerespectively equal to (0.5×integer) times the helical pitch p in thehelical structure consisting of the liquid crystalline molecules, or asecond alignment layer 16A as shown in FIGS. 5(C) and 5(D) is employed.In the case where a second alignment layer 16A is employed, this layeris brought into contact with the surface of the first retardation layer42′ that is on the side opposite to the alignment layer 16, or with thesurface of the second retardation layer 44′ facing the surface of thefirst retardation layer 42′.

[0152] Next, polarization elements including the retardation opticalelements 10, 20, 30 and 40 according to the aforementioned embodimentswill be described with reference to FIG. 10.

[0153] As shown in FIG. 10, a polarization element 50 includes apolarizing layer 51, and a retardation optical element 10 (20, 30, 40)arranged on the light-entering-side surface of the polarizing layer 51.Although the retardation optical element 10 (20, 30, 40) and thepolarizing layer 51 are depicted in FIG. 10 as being separated from eachother, they are actually in the state of being adhered to each other.

[0154] If the polarizing layer 51 is adhered to the retardation opticalelement 10 (20, 30, 40), the reflection of light on the retardationoptical element 10 (20, 30, 40) is remarkably decreased. Therefore, theappearance of bright and dark fringes is effectively prevented, and, atthe same time, contrast is improved. It is thus possible to effectivelyprevent lowering of display quality.

[0155] It is herein preferable that the directions 52 of the directorsof the liquid crystalline molecules on the one surface(light-entering-side surface) of the retardation optical element 10 (20,30, 40) and the directions 53 of the directors of the liquid crystallinemolecules on the other surface (light-emerging-side surface) of theretardation optical element 10 (20, 30, 40) be substantially parallelwith or perpendicular to the axis 54 of absorption of the polarizinglayer 51.

[0156] Further, the retardation optical elements 10, 20, 30 and 40according to the aforementioned embodiments can be incorporated inliquid crystal displays 60 as shown in FIG. 11, for example.

[0157] The liquid crystal display 60 shown in FIG. 11 includes apolarizer 102A on the light-entering side, a polarizer 102B on thelight-emerging side, and a liquid crystal cell 104.

[0158] Of these component parts, the polarizers 102A and 102B are soconstructed that they selectively transmit only linearly polarized lighthaving the plane of vibration in a predetermined direction, and arearranged in the cross nicol disposition so that the direction ofvibration of the linearly polarized light transmitted by the polarizer102A is perpendicular to that of vibration of the linearly polarizedlight transmitted by the polarizer 102B. The liquid crystal cell 104includes a large number of cells corresponding to pixels, and is placedbetween the two polarizers 102A and 102B.

[0159] It is herein preferable that the directions 52 of the directorsof the liquid crystalline molecules on the one surface(light-entering-side surface) of the retardation optical element 10 (20,30, 40) be parallel with the axis 51 of absorption of the polarizer 102Aarranged on the light-entering side and be perpendicular to the axis 54of absorption of the polarizer 102B arranged on the light-emerging side.It is also preferable that the directions 53 of the directors of theliquid crystalline molecules on the other surface (light-emerging-sidesurface) of the retardation optical element 10 (20, 30, 40) beperpendicular to the axis 51 of absorption of the polarizer 102Aarranged on the light-entering side and be parallel with the axis 54 ofabsorption of the polarizer 102B arranged on the light-emerging side.

[0160] In the liquid crystal display 60, the liquid crystal cell 104 isof VA mode, which a nematic liquid crystal having negative dielectricanisotropy is sealed in a liquid crystal cell. Linearly polarized lightthat has passed through the polarizer 102A arranged on thelight-entering side passes, without undergoing phase shift, throughthose cells in the liquid crystal cell 104 that are in the non-drivenstate, and is blocked by the polarizer 102B on the light-emerging side.On the contrary, when the linearly polarized light passes through thosecells in the liquid crystal cell 104 that are in the driven state, itundergoes phase shift, and this phase-shifted light passes through andemerges from the polarizers 102B arranged on the light-emerging side inan amount corresponding to the amount of this phase shift. It istherefore possible to display the desired image on the polarizer 102Bside (i.e., on the light-emerging side) by properly controlling thedriving voltage that is applied to each cell in the liquid crystal cell104.

[0161] In the liquid crystal display 60 having the above-describedconstruction, the retardation optical element 10 (20, 30, 40) accordingto the above-described embodiment is placed between the liquid crystalcell 104 and the polarizer 102B on the light-emerging side (thepolarizer capable of selectively transmitting light emerging from theliquid crystal cell 104, the light being in the predetermined state ofpolarization). Of the light emerging from the liquid crystal cell 104, apart of the light in the predetermined state of polarization thatslantingly emerges in the direction deviating from the normal of theliquid crystal cell 104 can be optically compensated by the retardationoptical element 10 (20, 30, 40) for the state of polarization.

[0162] As mentioned above, according to the liquid crystal display 60having the above-described construction, the retardation optical element10 (20, 30, 40) according to the above-described embodiment is placedbetween the liquid crystal cell 104 and the polarizer 102B on thelight-emerging side so that, of the light emerging from the liquidcrystal cell 104, a part of the light that slantingly emerges in thedirection deviating from the normal of the liquid crystal cell 104 canbe optically compensated by the retardation optical element for thestate of polarization. It is therefore possible to prevent theappearance of bright and dark fringes on the liquid crystal display 60and to improve contrast, while effectively eliminating the viewing angledependency problem. There can thus be prevented the lowering of displayquality.

[0163] The liquid crystal display 60 shown in FIG. 11 is of transmissiontype, which light is transmitted from one side to the other in thedirection of thickness. The present embodiment is not limited to this,and the retardation optical element 10 (20, 30, 40) according to theaforementioned embodiment may be incorporated in a liquid crystaldisplay of reflection type.

[0164] Further, in the liquid crystal display 60 shown in FIG. 11, theretardation optical element 10 (20, 30, 40) according to theabove-described embodiment is placed between the liquid crystal cell 104and the polarizer 102B on the light-emerging side. However, depending onthe type of optical compensation required, the retardation opticalelement 10 (20, 30, 40) may be placed between the liquid crystal cell104 and the polarizer 102A on the light-entering side. Furthermore, theretardation optical element 10 (20, 30, 40) may be arranged on bothsides of the liquid crystal cell 104 (between the liquid crystal cell104 and the polarizer 102A on the light-entering side, and between theliquid crystal cell 104 and the polarizer 102B on the light-emergingside). It is noted that not only one but also two or more retardationoptical elements may be placed between the liquid crystal cell 104 andthe polarizer 102A on the light-entering side, or between the liquidcrystal cell 104 and the polarizer 102B on the light-emerging side.

EXAMPLES

[0165] The aforementioned embodiments of the invention will now beexplained more specifically by referring to the following Examples andComparative Examples.

Example 1

[0166] In Example 1, a single retardation layer was made frompolymerizable monomer molecules, where the thickness of the retardationlayer was made uniform in order to make the directions of the directorsof the liquid crystalline molecules the same. In Example 1, the singleretardation layer was formed on a glass substrate.

[0167] A toluene solution was prepared by dissolving, in toluene, 90parts of a monomer containing, in its molecule, polymerizable acrylatesat both ends and spacers between mesogen existing at the center and theacrylates, having a nematic-isotropic transition temperature of 110° C.(a monomer having a molecular structure represented by the abovechemical formula (11)) and 10 parts of a chiral agent having, in itsmolecules, polymerizable acrylates at both ends (a compound having amolecular structure represented by the above chemical formula (14)). Tothis toluene solution, a photopolymerization initiator (“Irgacure® 907”available from Ciba Specialty Chemicals K.K., Japan) was added in anamount of 5% by weight of the above-described monomer. (With respect tothe chiral nematic liquid crystal thus obtained, it was confirmed thatthe directors of the liquid crystalline molecules on the surface of theliquid crystal layer that was in contact with the surface of thealignment layer were in one direction with a deviation of ±5 degrees.)

[0168] On the other hand, a transparent glass substrate was spin-coatedwith polyimide (“Optomer® AL1254” manufactured by JSR Corporation,Japan) dissolved in a solvent. After drying, a film of the polyimide(film thickness: 0.1 μm) was formed at 200° C., and was rubbed in onedirection so that it could function as an alignment layer.

[0169] The glass substrate coated with the alignment layer was set in aspin-coater, and was spin-coated with the toluene solution prepared bydissolving above-described monomer and other components in toluene,under the conditions that the thickness of the resulting film would beas uniform as possible.

[0170] The toluene contained in the above toluene solution was thenevaporated at 80° C. to form a coating film on the alignment layer. Itwas visually confirmed by the selective reflection of light that thiscoating film was cholesteric.

[0171] Ultraviolet light was applied to the above coating film, and withradicals thus released from the photopolymerization initiator containedin the coating film, the acrylates in the monomer molecules werethree-dimensionally crosslinked and polymerized to obtain asingle-layered retardation optical element. The thickness of the coatingfilm was 2 μm±1.5%. By the measurement made by using aspectrophotometer, it was found that the central wavelength of theselective reflection wave range of the coating film was 280 nm.

[0172] The retardation optical element thus produced was subjected tomeasurements using an automatic birefringence measuring apparatus(“KOBRA® 21ADH” manufactured by Oji Scientific Instruments K.K., Japan).As a result, the phase shift that occurred in the direction of plane wasfound to be several nanometers, this value being within the limit oferror of the measuring apparatus, and the phase shift that occurred inthe direction of thickness was found to be approximately 100 nm. It wasthus confirmed that the retardation optical element was functioning as anegative C plate.

[0173] Further, as shown in FIG. 12, linear polarizers 70A and 70B werearranged in the cross nicol disposition, and the retardation opticalelement 10 thus produced was placed between them and was visuallyobserved. The bright and dark fringes observed on the plane were veryfew.

Example 2

[0174] In Example 2, a single retardation layer of polymerizable monomermolecules was formed on a polymeric film. Namely, a retardation opticalelement was produced in the same manner as in Example 1, provided that aPVA solution prepared by dissolving 2% by weight of PVA in pure waterwas applied to a transparent TAC film by bar coating and was dried,after which a film (film thickness: 0.2 μm) was formed at 100° C. andwas rubbed in one direction so that it could function as an alignmentlayer. The retardation optical element thus produced was subjected tothe same measurements as those made in Example 1. The results of themeasurements were found to be similar to those obtained in Example 1.

COMPARATIVE EXAMPLE 1

[0175] In Comparative Example 1, a single retardation layer was madefrom polymerizable monomer molecules, where the thickness of theretardation layer was made non-uniform in order to make the directionsof the directors of the liquid crystalline molecules different from oneanother. Namely, a retardation optical element was produced in the samemanner as in Example 1, provided that the thickness of the retardationlayer was made 2 μm±5% by changing the settings of the spin-coater. Theretardation optical element thus produced was visually observed in thesame manner as in Example 1. As a result, bright and dark fringes wereclearly observed on the plane.

COMPARATIVE EXAMPLE 2

[0176] In Comparative Example 2, the surface of an alignment layer onwhich a single retardation layer of polymerizable monomer moleculeswould be formed was rubbed in various directions in order to make thedirections of the directors of the liquid crystalline moleculesdifferent from one another. Namely, a retardation optical element wasproduced in the same manner as in Example 1, provided that the surfaceof the alignment layer was rubbed in various directions. The retardationoptical element thus produced was visually observed in the same manneras in Example 1. As a result, bright and dark fringes were clearlyobserved on the plane.

Example 3

[0177] In Example 3, a single retardation layer was made frompolymerizable monomer molecules, where the thickness of the retardationlayer was made uniform and the helical pitch was made constant in orderto make the directions of the directors of the liquid crystallinemolecules on the two opposite main surfaces of the retardation layerparallel with each other. Namely, a retardation optical element wasproduced in the same manner as in Example 1, provided that the thicknessof the retardation layer was so adjusted that the directions of thedirectors at the starting point and the end point of thecholesteric-regular molecular structure would be parallel with eachother, allowing for the refractive index of the material to be used. Theretardation optical element thus produced was observed in the samemanner as in Example 1. As a result, it was found that the bright anddark fringes observed on the plane were obviously fewer than thosefringes observable in the case where the thickness of the retardationoptical element was not made as described above.

[0178] The linear polarizers 70A and 70B arranged on both sides of theretardation optical element 20 (see FIG. 12) were respectively rotated,and visual observation was made to determine, by the intensity oftransmitted light, the angle made by the directions of the directors atthe starting point and the end point of the cholesteric-regularmolecular structure of the retardation optical element 20. As a result,it was confirmed that this angle was within ±5 degrees.

Example 4

[0179] In Example 4, multiple retardation layers were made frompolymerizable monomer molecules, where the total thickness of theretardation layers was made uniform in order to make the directions ofthe directors of the liquid crystalline molecules the same.

[0180] The retardation optical element produced in Example 1 was used asthe first retardation layer. The surface of this retardation opticalelement that was on the side opposite to the alignment layer wasspin-coated with a toluene solution prepared in the same manner as inExample 1, at a number of revolutions greater than that in Example 1.

[0181] Next, the toluene contained in the toluene solution wasevaporated at 80° C. to form a film on the first retardation layer. Thiscoating film was visually observed, and it was confirmed by theselective reflection of light that the coating film was cholesteric.

[0182] Ultraviolet light was applied to the above coating film, and withradicals thus released from the photopolymerization initiator containedin the coating film, the acrylates in the monomer molecules werethree-dimensionally crosslinked and polymerized to form a secondretardation layer. There was thus produced a multi-layered retardationoptical element. The total thickness of this retardation optical elementwas 3.5 μm±1.5%. From the measurement made by using a spectrophotometer,it was found that the central wavelength of the selective reflectionwave range of the retardation optical element composed of the multipleretardation layers was 280 nm.

[0183] The cross section of the multiple retardation layers was observedby a transmission electron microscope. As a result, the bright and darkfringes that appeared on the polymerized retardation layers were foundto be parallel with each other (from this, it can be known that thedirections of the helical axes agree with each other). In addition, nodiscontinuity was found between the retardation layers (from this, itcan be known that the directions of the directors of the liquidcrystalline molecules on the two adjacent surfaces of the neighboringretardation layers coincide with each other).

[0184] Further, as shown in FIG. 12, linear polarizers 70A and 70B werearranged in the cross nicol disposition, and the above-obtainedretardation optical element 40 was placed between them and was visuallyobserved. The bright and dark fringes observed on the plane were veryfew.

COMPARATIVE EXAMPLE 3

[0185] In Comparative Example 3, multiple retardation layers were madefrom polymerizable monomer molecules, where the total thickness of theretardation layers was made non-uniform in order to make the directionsof the directors of the liquid crystalline molecules different from oneanother. Namely, a retardation optical element was produced in the samemanner as in Example 3, provided that the total thickness of theretardation layers was made 3.5 μm±5% by changing the settings of thespin-coater. The retardation optical element thus produced was visuallyobserved in the same manner as in Example 3. As a result, bright anddark fringes were clearly observed on the plane.

Example 5

[0186] In Example 5, multiple retardation layers were made from liquidcrystalline polymers, where the total thickness of the retardationlayers was made uniform in order to make the directions of the directorsof the liquid crystalline molecules the same.

[0187] A toluene solution was prepared by dissolving, in toluene, aliquid crystalline polymer containing acrylic side chains, having aglass transition temperature of 80° C. and an isotropic transitiontemperature of 200° C. (With respect to the polymeric, cholestericliquid crystal thus obtained, it was confirmed that the directors of theliquid crystalline molecules on the surface of the liquid crystal layerthat was in contact with the surface of the alignment layer were in onedirection with a deviation of ±5 degrees.)

[0188] On the other hand, polyimide (“Optomer® AL1254” manufactured byJSR Corporation, Japan) dissolved in a solvent was applied to atransparent glass substrate by spin-coating and was dried, after which afilm (film thickness: 0.1 μm) was formed at 200° C. and was rubbed inone direction so that it could function as an alignment layer.

[0189] The glass substrate coated with the alignment layer was set in aspin-coater, and was spin-coated with the toluene solution prepared bydissolving the above-described liquid crystalline polymer in toluene,under the conditions that the thickness of the resulting film would beas uniform as possible.

[0190] The toluene contained in the above toluene solution was thenevaporated at 90° C. to form, on the alignment layer, a coating film,which was held at 150° C. for 10 minutes. This coating film was visuallyobserved, and it was confirmed by the selective reflection of light thatthe coating film was cholesteric. Subsequently, the coating film wascooled to room temperature to make the liquid crystalline polymer into aglassy state and to fix it to this state, thereby forming a firstretardation layer. The thickness of this retardation layer was 2μm±1.5%. By the measurement made by using a spectrophotometer, it wasconfirmed that the central wavelength of the selective reflection waverange of the first retardation layer was 370 nm.

[0191] To the first retardation layer that had been made into and fixedto a glassy state, a liquid crystalline polymer containing acrylic sidechains, having a glass transition temperature of 75° C. and an isotropictransition temperature of 190° C., dissolved in toluene, was applied byspin-coating at a number of revolutions greater than before.

[0192] The toluene contained in the above toluene solution was thenevaporated at 90° C. to form a film, which was held at 150° C. for 10minutes. This coating film was visually observed, and it was confirmedby the selective reflection of light that the coating film wascholesteric. Subsequently, this coating film was cooled to roomtemperature to make the liquid crystalline polymer into a glassy stateand to fix it to this state, thereby forming a second retardation layer.Thus, there was obtained a multi-layered retardation optical element.The total thickness of this retardation optical element was 3.5 μm±1.5%.By the measurement made by using a spectrophotometer, it was found thatthe central wavelength of the selective reflection wave range of themulti-layered retardation optical element was 370 nm.

[0193] The cross section of the multiple retardation layers was observedby a transmission electron microscope. As a result, the bright and darkfringes that appeared on the fixed retardation layers were found to beparallel with each other (from this, it can be known that the directionsof the helical axes agree with each other). In addition, nodiscontinuity was found between the retardation layers (from this, itcan be known that the directions of the directors of the liquidcrystalline molecules on the two adjacent surfaces of the neighboringretardation layers coincide with each other). Further, in themeasurement made by a spectrophotometer, no optical peculiarity wasobserved in transmittance.

[0194] Linear polarizers 70A and 70B were arranged in the cross nicoldisposition, as shown in FIG. 12, and the retardation optical element 40thus produced was placed between them and was visually observed. Thebright and dark fringes observed on the plane were very few.

COMPARATIVE EXAMPLE 4

[0195] In Comparative Example 4, multiple liquid crystal layers weremade from liquid crystalline polymers, where the total thickness of theliquid crystal layers was made non-uniform in order to make thedirections of the directors of the liquid crystalline moleculesdifferent from one another. Namely, a retardation optical element wasproduced in the same manner as in Example 5, provided that the totalthickness of the retardation layers was made 3.5 μm±5% by changing thesettings of the spin-coater. The retardation optical element thusproduced was visually observed in the same manner as in Example 5. As aresult, bright and dark fringes were clearly observed on the plane.

What is claimed is:
 1. A retardation optical element comprising aretardation layer having a cholesteric-regular molecular structure withliquid crystalline molecules in planar orientation, a helical pitch inthe molecular structure being so adjusted that a wavelength of lightselectively reflected by the retardation layer due to its molecularstructure falls in a range different from a wave range of incidentlight, wherein directions of directors of liquid crystalline moleculeson one surface of two opposite main surfaces of the retardation layerare substantially the same, and those of directors of the liquidcrystalline molecules on the other surface of the retardation layer arealso substantially the same.
 2. The retardation optical elementaccording to claim 1, wherein dispersion in the directions of thedirectors of the liquid crystalline molecules on each of the one surfaceand the other surface of the retardation layer is within ±10°.
 3. Theretardation optical element according to claim 1, wherein the directionsof the directors of the liquid crystalline molecules on the one surfaceof the retardation layer are substantially parallel with those of thedirectors of the liquid crystalline molecules on the other surface ofthe retardation layer.
 4. The retardation optical element according toclaim 3, wherein an angle made by the directions of the directors of theliquid crystalline molecules on the one surface of the retardation layerand those of the directors of the liquid crystalline molecules on theother surface of the retardation layer is within ±10°.
 5. Theretardation optical element according to claim 1, wherein theretardation layer has a helical structure with a pitch number ofsubstantially (0.5×integer) between the directions of the directors ofthe liquid crystalline molecules on the one surface of the retardationlayer and those of the directors of the liquid crystalline molecules onthe other surface of the retardation layer.
 6. The retardation opticalelement according to claim 5, wherein an angle made by the directions ofthe directors of the liquid crystalline molecules on the one surface ofthe retardation layer and those of the directors of the liquidcrystalline molecules on the other surface of the retardation layer iswithin ±10°.
 7. The retardation optical element according to claim 5,wherein the helical structure of the retardation layer has a helicalpitch or a pitch number that varies depending upon position in a planeextending in parallel with the one surface and the other surface of theretardation layer.
 8. The retardation optical element according to claim1, wherein the retardation layer is composed of successively, directlylaminated multiple layers, each having a cholesteric-regular molecularstructure with liquid crystalline molecules in planar orientation, anddirections of directors of the liquid crystalline molecules on twoadjacent surfaces of each two neighboring layers among the multiplelayers are substantially parallel with each other.
 9. The retardationoptical element according to claim 1, wherein the retardation layer hasa molecular structure in which chiral nematic liquid crystallinemolecules are three-dimensionally crosslinked.
 10. A method of producinga retardation optical element, comprising the steps of: applying a firstliquid crystal comprising at least one type of polymerizable monomer oroligomer molecules having cholesteric regularity to an alignment layerthat has been so formed that a surface thereof exerts alignmentregulation power in substantially one direction, thereby aligning thefirst liquid crystal by the alignment regulation power of the surface ofthe alignment layer; and three-dimensionally crosslinking andsolidifying the aligned first liquid crystal, thereby forming a firstretardation layer that selectively reflects light whose wavelength fallsin a range different from a wave range of incident light.
 11. The methodaccording to claim 10, wherein a thickness of the first liquid crystalthat is applied to the surface of the alignment layer is so adjustedthat directions of directors of the liquid crystalline molecules on asurface of two opposite main surfaces of the first retardation layer,which surface is not controlled by the alignment regulation power of thesurface of the alignment layer, are regulated.
 12. The method accordingto claim 10, wherein another alignment layer is brought into contactwith a surface of the first liquid crystal applied to the surface of thealignment layer, the contacting surface being on a side apart from thesurface of alignment layer, in order to regulate directions of directorsof the liquid crystalline molecules on the surface of two opposite mainsurfaces of the first retardation layer, which surface is not controlledby the alignment regulation power of the surface of the alignment layer.13. The method according to claim 10, further comprising the steps of:directly applying, to the first retardation layer, a second liquidcrystal comprising at least one type of other polymerizable monomer oroligomer molecules having cholesteric regularity, thereby aligning thesecond liquid crystal by the alignment regulation power of the surfaceof the first retardation layer; and three-dimensionally crosslinking andsolidifying the aligned second liquid crystal, thereby forming a secondretardation layer that selectively reflects light whose wavelength fallsin a range different from the wave range of incident light.
 14. Themethod according to claim 13, wherein, in at least one step of the stepof forming the first retardation layer and that of forming the secondretardation layer, a thickness of the first or second liquid crystalthat is applied to the surface of the alignment layer or of the firstretardation layer is so adjusted that directions of directors of theliquid crystalline molecules on a surface of two opposite main surfacesof the first or second retardation layer, which surface is notcontrolled by the alignment regulation power of the surface of thealignment layer or of the first retardation layer, are regulated. 15.The method according to claim 13, wherein, in at least one step of thestep of forming the first retardation layer and that of forming thesecond retardation layer, another alignment layer is brought intocontact with a surface of the first or second liquid crystal applied tothe surface of the alignment layer or of the first retardation layer,the contacting surface being on a side apart from the surface of thealignment layer or of the first retardation layer, in order to regulatedirections of directors of the liquid crystalline molecules on a surfaceof two opposite main surfaces of the first or second retardation layer,which surface is not controlled by the alignment regulation power of thesurface of the alignment layer or of the first retardation layer. 16.The method according to claim 13, wherein both of the first and secondliquid crystals that are applied to form the first and secondretardation layers, respectively, have selective reflection wave rangesthat are either shorter or longer than the wave range of incident light.17. The method according to claim 13, wherein the first and secondliquid crystals that are applied to form the first and secondretardation layers, respectively, comprise substantially the samematerial.
 18. A method of producing a retardation optical element,comprising the steps of: applying a first liquid crystal comprising aliquid crystalline polymer having cholesteric regularity to an alignmentlayer that has been so formed that a surface thereof exerts alignmentregulation power in substantially one direction, thereby aligning thefirst liquid crystal by the alignment regulation power of the surface ofthe alignment layer; and solidifying the aligned first liquid crystalinto a glassy state by cooling, thereby forming a first retardationlayer that selectively reflects light whose wavelength falls in a rangedifferent from a wave range of incident light.
 19. The method accordingto claim 18, wherein a thickness of the first liquid crystal that isapplied to the surface of the alignment layer is so adjusted thatdirections of directors of the liquid crystalline molecules on a surfaceof two opposite main surfaces of the first retardation layer, whichsurface is not controlled by the alignment regulation power of thesurface of the alignment layer, are regulated.
 20. The method accordingto claim 18, wherein another alignment layer is brought into contactwith a surface of the first liquid crystal applied to the surface of thealignment layer, the contacting surface being on a side apart from thesurface of the alignment layer, in order to regulate directions ofdirectors of the liquid crystalline molecules on a surface of twoopposite main surfaces of the first retardation layer, which surface isnot controlled by the alignment regulation power of the surface of thealignment layer.
 21. The method according to claim 18, furthercomprising the steps of: directly applying, to the first retardationlayer, a second liquid crystal comprising another liquid crystallinepolymer having cholesteric regularity, thereby aligning the secondliquid crystal by the alignment regulation power of the surface of thefirst retardation layer; and solidifying the aligned second liquidcrystal into a glassy state by cooling, thereby forming a secondretardation layer that selectively reflects light whose wavelength fallsin a range different from the wave range of incident light.
 22. Themethod according to claim 21, wherein, in at least one step of the stepof forming the first retardation layer and that of forming the secondretardation layer, a thickness of the first or second liquid crystalthat is applied to the surface of the alignment layer or of the firstretardation layer is so adjusted that directions of directors of theliquid crystalline molecules on a surface of two opposite main surfacesof the first or second retardation layer, which surface is notcontrolled by the alignment regulation power of the surface of thealignment layer or of the first retardation layer, are regulated. 23.The method according to claim 21, wherein, in at least one step of thestep of forming the first retardation layer and that of forming thesecond retardation layer, another alignment layer is brought intocontact with a surface of the first or second liquid crystal applied tothe surface of the alignment layer or of the first retardation layer,the contacting surface being on a side apart from the surface of thealignment layer or of the first retardation layer, in order to regulatedirections of directors of the liquid crystalline molecules on a surfaceof two opposite main surfaces of the first or second retardation layer,which surface is not controlled by the alignment regulation power of thesurface of the alignment layer or of the first retardation layer. 24.The method according to claim 21, wherein both of the first and secondliquid crystals that are applied to form the first and secondretardation layers, respectively, have selective reflection wave ranges,that are either shorter or longer than the wave range of incident light.25. The method according to claim 21, wherein the first and secondliquid crystals that are applied to form the first and secondretardation layers, respectively, comprise substantially the samematerial.
 26. A polarization element comprising: a polarizing layer; anda retardation optical element according to any of claims 1 to 9,provided on a surface of the polarizing layer.
 27. The polarizationelement according to claim 26, wherein the directions of the directorsof the liquid crystalline molecules on the one surface or the othersurface of the retardation optical element are substantially parallelwith or perpendicular to an axis of absorption of the polarizing layer.28. A liquid crystal display comprising: a liquid crystal cell; a pairof polarizers so arranged that the liquid crystal cell is sandwichedtherebetween; and a retardation optical element according to any ofclaims 1 to 9, placed between the liquid crystal cell and at least oneof the paired polarizers, wherein, of light in a predetermined state ofpolarization, emerging from the liquid crystal cell, a part of lightthat emerges slantingly in a direction deviating from the normal of theliquid crystal cell is compensated by the retardation optical elementfor the sate of polarization.
 29. The liquid crystal display accordingto claim 28, wherein the directions of the directors of the liquidcrystalline molecules on the one surface or the other surface of theretardation optical element are substantially parallel with orperpendicular to an axis of absorption of each one of the polarizers.